1. Field of the Invention
The invention relates to a commutator.
2. Description of the Prior Art
From International Patent Disclosure WO 02/19478 A1, a hook commutator for an electric motor armature is known. The known commutator has many spaced-apart metal segment support pieces, each with one securing portion that digs into a hub body and connected solidly and electrically conductively to a carbon contact segment, and the contact segments as a total form a brush running surface. The securing portion of each segment support piece is adjoined in the axial direction by an axial portion, on the end of which a winding connection hook is provided with which a winding wire can be connected electrically. In the production of the electric motor armature, one winding wire is wound in each winding connection hook. In a required connection process of the winding wire and winding connection hooks, a durably good mechanical and electrical connection quality of the winding connection hooks and winding wire is crucial. So-called hot staking is used as a connection process. In it, the winding connection hook is deformed in such a way that the winding wire is clamped in place. After that, an electrical voltage is applied, so that the winding connection hook and the winding wire heat up. In this process, an insulation layer detaches from the winding wire, and welding of the winding wire and winding connection hook takes place. It is also known from this reference, in the transition region between the axial portion and the securing portion of the segment support piece, to provide a region of reduced cross-sectional area, in order to reduce the thermal conduction from the winding connection hook to the securing portion, among other reasons in order to avoid an impairment of the soldered connection between the contact segment and a securing portion in the hot staking process.
In the production of the soldered connection between the carbon contact segments and the associated securing portions, problems repeatedly arise. This can be ascribed to the fact that in the liquid state of the solder, the intermolecular forces of adhesion between the liquid solder and the contact segment and/or between the solder and the metal securing portion are greater than the intermolecular forces of cohesion within the solder. This causes a capillary diffusion of the liquid solder into surface regions not moistened by the liquid solder—above all in the peripheral and corner regions of the carbon segment and securing portion. Often, solidifying droplets of solder even protrude laterally. They protrude partly past the air gap between two adjacent securing portions and thus cause dangerous electrical short circuits. It also happens that protruding solder particles, in operation of the finished electrical machine, come loose and reach the region of the motor winding, where they cause short circuits. Also, a fuel pump through which fuel is flowing and which is equipped with the known commutator can be damaged by detaching solder particles. To avoid laterally protruding solder particles, attempts are made to reduce the quantity of solder. However, this leads to unwanted reduced strength and reduced electrical conductivity of the connections comprising the contact segments and the associated securing portions.